PT96014B

PT96014B - PROCESS AND PACKAGE OF LIGACATION USING AN ELECTRICAL RESISTANCE FOR WELDING ELEMENTS OF PLASTIC MATERIAL

Info

Publication number: PT96014B
Application number: PT96014A
Authority: PT
Inventors: Denis Dufour; Francois Fortin
Original assignee: Gaz De France
Priority date: 1989-11-29
Filing date: 1990-11-28
Publication date: 1998-07-31
Also published as: CN1028161C; JPH03213328A; MC2160A1; EP0430761B1; DE69019114D1; DE69019114T2; FR2654977B1; ATE121990T1; CA2031025A1; CN1052630A; PT96014A; US5182440A; EP0430761A2; EP0430761A3; FR2654977A1

Abstract

The invention relates to the welding of components made of heat-fusing plastic, using an electrical heating resistor arranged in the thickness of a connection component. According to the invention, the resistor is a thin electrically conductive layer advantageously formed on a supporting film made of heat-fusing plastic and capable of causing the tearing of the layer at a specific temperature corresponding to the welding temperature of the components. The invention is used particularly for the thermal welding of polyethylene pipes used in the gas industry.

Description

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The welding operation is carried out by placing the parts of the parts to be welded together and connecting the wound wire to a source of electric current (such as a rectifying alternating current source), which, by Joule effect, will heat the resistance and to cause the softening up to the melting of the plastic material surrounding the parts, thus realizing the welding *

In order for this weld to be of good quality, ie to obtain a gas-tight seal and a satisfactory mechanical strength, the heating time must be between a minimum duration to obtain, after cooling, a correct weld between the welds. parts, and a maximum duration shorter than that which is liable to cause a thermal degradation of the parts. With the current resistances of the type of electric wire wound, it has been noticed that in a number of cases the fusion and the consecutive pressure of the plastic material of the parts induce contacts between turns with the creation of short circuits, suitable to induce just thermal degradations of material.

In current welding systems, junction defects may also appear, taking into account the relative imprecision of the principles used to determine the optimum heating duration corresponding to " welding time ", i.e., the time during which the electrical resistance goes be supplied with electric current *

When the welding time is set automatically, the welding stop is often obtained with the aid of sensors which are arranged in wells formed in the joint at localized sites of the welding zone and at a not negligible distance from the electric winding heating wire 'Given the spacing between these wells, their arrangement and the relatively low thermal conductivity of the plastic materials used, if short circuits occur, they can at best be detected only with a certain delay.

We will also note that the

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(1) and (2), and (2), and (2), and (2), and (4) The 4 '''''''''''''''''''' In addition, the invention relates to a process for the preparation of a compound of the formula: ## STR1 ## ## STR3 ## tb______________________________________ tb In the preferred embodiment of the present invention, the invention relates to a method according to the invention. if it is desired, then, diethyl ether and polypropylene glycols.

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Smgsftáa * Istos ^ ío # * * il! The title compound was prepared by the method of the invention in which the compound of the formula (II): ## STR1 ## is replaced by the group consisting of a compound of the formula: ## STR1 ## teaspoon AII of this is also disclosed; for example, by the addition of the aforesaid polyurethane by the addition of the polypropylene or polypropylene to the polypropylene or polypropylene. plastic material in the form of plastic wrappers and plastic wrappers, the plastic wrapper, the plastic wrapper, the plastic wrapper, the plastic wrapper and the plastic wrapper. 4 'as well as'4' asylum at the same time as the skin and the skin. The first section of the first section of the first section shows the first section of the first section of the first section of the second section of the second section. The wells are placed at the top of the roof at the top of the roof and at the top of the roof. 'For the purposes of this Directive' shall mean the following: 'llllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll' the aliphatic hydrochloric acid, which is the same as that of the other organic carbonate esterified in the second part of the first step of the first step in the preparation of the first step in the preparation of the first step, fasar eireslar «ata corraata s grate ha xellia

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I until it causes a continuous slit through the latter with discontinuity of sheet material, inducing the stopping of heating! By interruption of the current, it will be noted that the expression " welding temperature " the temperature to be achieved by the parts to be joined must be interpreted as defined; site of its welding zone (i.e., in the vicinity of the

ji its junction interface) so that during the warm-up time; these parts are locally melted, and that, after heating and cooling parts are attached in a subus- gases and this with a mechanical resistance compatible with its use.

Other explanations, features and advantages of the present invention will still emerge in the following description, with reference to the accompanying drawings, which figures show: FIG. 1 shows a schematic cross-sectional view of a connection system according to the present invention with a sleeve for the top-to-top connection of two tubes; ii | Figure 2 is a schematic perspective view of a possible embodiment of the resistive element shown in the present invention; Figure 3 is a cross-sectional illustration of a variant embodiment of the system shown in Figure 1, using in this case a branch socket for a transverse union in a tube; and | FIG. 4 is an enlarged local view of a variant embodiment of the resistive element shown in FIG. Referring first to Figure 1, there is thus shown an electro-weldable joint j'with the general reference 1, comprising a joint sleeve j (2) provided with a body of thermofusible plastic material, the central hole (4) passing through it from one side to the other is adapted to receive, to join them, two substantially coaxial tubes (6, 8), with a slightly outer diameter. . less than the diameter of the hole (4) of the sleeve

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The two tubes 6 and 8 are engaged within the bore 4 of the sleeve at one of its ends. These tubes extend a length 1 and along the surfaces 6a and 8a, , in front of a zone of this sleeve (denominated zone of welding). This zone is bounded by the contiguous outer surface (2a) and comprises an electric heating resistor (10) connected by two | connecting terminals 12 and 14 to a power source (not shown), such as a rectifier alternating current source, Among the plastic materials usable for making the sleeve body and the pipes to be joined, there may be mentioned, in particular, polyethylene, polyamide, poly- butylene and polypropylene.

According to the present invention, and as can be seen from the figures, the electric heating resistor consists of a layer or sheet of electrically conductive material 11. The sheet 11 can be formed, in particular by spraying tank (13) of thermofusible plastic material.

Preferably, the plastic material constituting the carrier film 13 will be different from that of the connecting piece 2 and the tubes. More precisely, it will be generally preferable to use for the film 13 a material plastic with a higher melting point of

I that of the plastic material of the tubes and the body of the piece of union. In addition, it is preferred to choose for this purpose a material which, when the film is still in the solid state, has a coefficient of thermal expansion intermediate the jo of the conductive layer 11 (solid state) and that of the tubes and In this case, by choosing a layer of electrically conductive material (11) which is capable of melting at the welding temperature of the parts, it will be possible to ensure a good self-regulation of the weld. As long as the flow of the stream in the layer does not raise the temperature of the film to its melting temperature, the stream I will circulate normally and the parts will be heated. But when the softening temperature is reached, and after melting, the material constituting the carrier film is expanded, first causing cracks in the conductive layer and then the appearance of a continuous slit from one side to the other at full thickness of this camad a, resulting in the interruption of heating by cutting the current. It is evident that the use of such a system has several advantages over the conventional conductor winding and, in particular: - elimination of short-circuit risks, - more even heating of the parts, where the heat exchange surface between the heating element and the parts to be joined is markedly increased, - a reduction of cost of the realization of the pieces of union, which no longer need the use of sensors

II, - a better location of the heating flow in the vicinity of the welding interface, in that the thickness of the conductive sheet can be in the range of a few hundred angstroms, while the diameter of a conductive wire is typically of the order of millimeters, - finally, the use of such a resistive layer makes it possible to make a truly self- since it defines by itself the time during which there is current passing in the immediate vicinity of the welding zone and therefore under the best possible conditions of reliability and effectiveness. . As will be understood, the embodiment ' in particular: - the nature of the conductive material (usually a metal) constituting the thin layer (11), - the thickness of this layer, I Φ - if necessary, the thickness and nature of the (13), - the dimensions and geometry of the heating element as a whole, - the dimensions and geometry of the heating element as a whole,

Once all these choices have been made, it is then necessary to make reliable and industrially achievable electrical contacts which enable the heating element thus made to be supplied with power.

They are considered successively | these different criteria. (a) The nature of the conductive material used, the thickness of the foil and the geometry of the heating element. These different parameters must be chosen in order to obtain a resistance which will allow: i to reach the welding zone of the parts, the temperature of

I suitable welding *

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For a connection between a polyethylene sleeve and also polyethylene pipes, it is practically necessary to achieve in the vicinity of the contiguous joining surfaces of the parts (with reference numbers 2a, 6a and 8a respectively in the figures) temperatures understood! between about 150-350 and 400 ° C, for a period of time of the order of a few minutes. Knowing the welding voltage and the electrical resistance of the heating element, the electric power dissipated at the junction will determine the rate of rise of temperature. I. i; The heating time will therefore not be a predetermined parameter. IA resistance of the element cale factor is function of electrical resistivity of the metal used | the thickness of the conductive layer, the cross- current in the layer and the distance separating the electrical contacts, so that we can easily calculate the thickness of the metallized layer and choose the nature of the conducting metal in order to obtain the value of the electrical resistance that allows to attain the desired temperatures, in the knowledge that in the gas industry, in particular, a voltage is usually used; welding on the order of 39 V.

Claims

In general, the thickness of the conductive layer will be between about 10 ° and 10 °. The conductive material constituting this layer will advantageously be chosen in such a way that the temperature of the conductive layer is between 10 ° and 10 °. As far as the geometry of the heating element is concerned, this will of course vary depending on the desired application. In the case of FIG. 1, that is, for one | (10) (as shown in FIG. 2), a sleeve was made in the thickness of which the sheet I was included. which is in the form of an axis cylinder 11 substantially coincident with the axis 4a of the central hole 4 of the sleeve. In view of the constitution of this resistive element, it may be integrated in the immediate vicinity of the inner surface (2a) of the joint, possible therefore of the outer surfaces of the joint | (6a) and (8a) in front of the two tubes, They could however face each other! other embodiments,! | For example, in the case (shown in FIG. 3) of the joining of a pipe such as (16) and of a tapping socket such as (18) locally recapping the tube through a saddle (22), the The resistive layer 20, constituted as above, has a curved, rectangularly parallelepipedal planar shape, in the manner of a saddle. After welding and cooling the parts, a central hole (24) corresponding to the orifice (26) of the tube through which it communicates with the inner passage (28) of the tube is opened. It is clear that the resistive layer 20 as above, attached to two connecting terminals, such as 32, is connected to the connecting rod 30, and (34) for their electrical power supply. trica. - 8 -

Whatever the intended application, it will be preferred to ensure a mechanical resistance to the joining of one side and the other of the resistive element, to puncture; the electrically conductive layer and the mode carrier film; that the element has holes or openings (36) (fig. 2) which pass through it side by side, these holes being, once the connecting piece is made, filled by the plastic material | j of this part, thus allowing to ensure a local continuity ! i || of the material »| As shown in Fig. 4, || it can also be envisaged that the conductive layer 11 is shown in the form of a metal grid or a perforated body! I is made as a conductive knitted net deposited in a thin layer in the carrier film, in which case the meshes (38) or holes of the grid or net are still filled by the plastics material of the connecting piece, such as the holes (39) they have made in correspondence through the support film (13). As is understood, the film of FIG.

j | (13) of the electrically conductive layer has the function, if it is provided, to interrupt the heating of the parts by tearing the layer (11) deposited thereon. In practice, this rupture will be caused by the melting with placing the carrier film under i; pressure. I: | Therefore, a hot-melt plastic material having a melting point will be chosen for the film. are such that the expansion of the film does not result in tearing of the conductive layer 11 other than at the time when the welding temperature has been reached in the vicinity of the junction interface of the parts. The studies which may be carried out so far in connection with the welding of pipes and polyethylene joint pieces have shown that the welding temperatures to be attained are of the order of 150 to 250 ° C and for heating rates of the order of 20 to 100 ° c / m. SB-9-

In general, therefore, the carrier film will be a film consisting of a polymeric material having a melting temperature of at least greater than about 200Â ° C. Among the polymers which may be considered, for example, polyester, polyamide 6, fluorinated polymers (for example polytetrafluoroethylene), crystalline polycarbonate, polysulfide: phenylene and polyamides may be mentioned. In a general way, and by the! less in the case of joining pieces made of polyethylene, choice of thermofusible plastic materials having a melting temperature of less than about 400 ° C will be preferred in order to avoid: any risk of damage to the parts by overheating · | In addition to the nature of the backing film, its thickness will also be an important choice. In most applications, it will be in the range of about 5 to 100 micrometers (i.e., 5 to 100Â ° -10-6 m) and preferably equal to about 10 micrometers. c) Realization of the electrical stations I I; In order to ensure the connection of the resistive element it was necessary to make ohmic electrical switches in the thin conductive film (11). For this purpose, adhesives, tapes or metal deposits, electric conductors, have been used in order to obtain lateral electric connectors, as shown in (15) and (17) in the figures. When the couplings have been made, the electrical wires (19) and (21) of connection I may be welded to the corresponding connection terminals, d) Creation of a cold zone l | In particular in the case of the top-to-top union of two tubes through a connecting sleeve (fig. 1)! it has further proved useful to form a " cold zone " in front of the ends of the facing tubes, in order to prevent that! in the course of heating or welding may flow out;

(e) separating the tubes, causing them to partially obstruct them. For this, the example given in fig. 1 is provided with a surface (11) on the surface of the conductive layer (11) which carries the protection electricity, extending in front of the space (e) (Figure 1). | For it to perform its function, i! this jamb will be made of a material, preferably metal, with a melting temperature above the melting temperature of the surrounding plastic material and of the materials constituting the plastic film 13 and even the conductive layer i | In general, the thickness I of the barrette will be between 3 and 5 micrometers. The basis of what has just been set forth is that different work carried out by the applicant has allowed it to be used. define the complete (but not limiting) example below,! which allows to realize a resistive element that can be | used in a polyethylene connecting piece for the leak-tight union of polyethylene pipes. Composition: i - Polyester film support film II | l of about 12 micrometers thick, | aluminum conductive layer of about 200 A (i.e., 200 x 10 m), I: - Geometry of the heating element: sheet of aluminum; 10 x 10 cm ^, with holes that give it the appearance of a knit net. i - Connections through 30-mm copper tapes | 1 cm thicknesses on which a silver lacquer was applied.

2 - Heating power of folhai 0.015 w / mm. Results After about 200 s, the maximum temperature of the metal layer is about 200 ° C. The heating is automatically interrupted by tearing the metal layer, .1 about 250 s. - 11 1 I

r: ϋ- ', "7'; λ | It should be understood that it would be possible, without departing from the scope of the present invention, to use any suitable means (other than the plastic film) susceptible according to the present invention, | In particular it would be possible, by adapting the thickness and nature of this conductive sheet, to dispense with the use of the carrier polymer film (13), whereby the resistance (11) is designed to melt-rupture at a temperature comprised between the melting temperature of the plastic material of the joint and the elements to be joined and a maximum temperature of degradation of these same parts. that the temperature of degradation or breakage of the molecular chains making up a part is reached when there are projections of melt and / or fumes. The presence of cavities inside the parts and also the sign of such degradation, such as the finding of a too deep melt zone with risks of leakage at the level of the weld. ! 12 -